Method of forming pixel sensor cell having reduced pinning layer barrier potential

Abstract

A method of forming a pixel sensor cell structure. The method of forming the pixel cell comprises forming a doped layer adjacent to a first side of a transfer gate structure for coupling a collection well region and a channel region. Potential barrier interference to charge transfer caused by a pinning layer is reduced.

1. A method of forming a pixel sensor cell comprising the steps of:
 a) providing a semiconductor substrate; 
 b) forming a gate structure on said substrate; 
 c) forming a pinning layer comprising material of a first conductivity type in said substrate; 
 d) forming a collection well region comprising material of a second conductivity type beneath said pinning layer; 
 e) forming a gate diffusion region of a second conductivity type in said substrate adjacent a second side of said gate structure, said gate structure forming a channel region enabling charge transfer between said collection well region and said diffusion region; and 
 f) forming a doped layer in a different step than said step of forming said collection well region, said doped layer comprising material of said second conductivity type adjacent to said first side of said gate structure for coupling said collection well region and said channel region to reduce potential barrier interference to charge transfer caused by said pinning layer. 
 
   
   
     2. The method of  claim 1 , wherein said step (c) of forming said pinning layer comprises the steps of:
 forming a layer of material over a surface of said substrate and said gate structure to provide a first edge spaced a distance away from said first side of said gate structure; and 
 
     forming said pinning layer having an edge in alignment with said first edge. 
   
   
     3. The method of  claim 1 , wherein an edge of said collection well region is formed substantially beneath said first side of said gate structure and offset from said edge of said pinning layer. 
   
   
     4. The method of  claim 2 , wherein said step (d) of forming said collection well region comprises ion implanting material of a second conductivity type at a substantially vertical angle relative to said surface of said substrate and ion implanting material of a second conductivity type at an angle less than vertical relative to said surface of said substrate. 
   
   
     5. The method of  claim 2  further comprising the steps of:
 prior to said step of forming said pinning layer, removing portions of said layer of material to form a spacer structure adjacent sidewalls of said gate structure, wherein an edge of said spacer structure defines said first edge. 
 
   
   
     6. The method of  claim 5  further comprising the steps of:
 prior to said step (d) of forming said collection well region, removing at least said spacer structure adjacent said first side of said gate structure; and 
 ion implanting material of a second conductivity type at a substantially vertical angle relative to said surface of said substrate to form said collection well region. 
 
   
   
     7. The method of  claim 2 , wherein said layer of material comprises borosilicate glass (BSG). 
   
   
     8. The method of  claim 1 , wherein said step (f) of forming said doped layer comprises ion implanting material of a second conductivity at an angle less than vertical relative to a surface of said substrate. 
   
   
     9. The method of  claim 1 , wherein said step (f) of forming said doped layer comprises forming a portion of said doped layer in direct physical contact with said channel region. 
   
   
     10. The method of  claim 1 , wherein said step (d) of forming said collection well region comprises a first ion implanting step and said step (f) of forming said doped layer comprises a second ion implanting step different than said first ion implanting step. 
   
   
     11. The method of  claim 1 , wherein said step (d) of forming comprises doping said collection well region at a first dopant concentration and said step (f) of forming comprises doping said doped layer at a second dopant concentration.